The present invention relates generally to push-button type tuning apparatuses, and more particularly to a push-button type tuning apparatus in which a V-shaped cam part is provided on a memory piece which is rotatably supported on a push-button assembly, and a projecting cam part is simply provided on a cam plate which is slidable in a direction perpendicular to the inserting direction of the push-button assembly, to increase the slidable range of the cam plate and improve the tuning accuracy, by urging the V-shaped cam part and the projecting cam part to mutually make contact with each other and restricting these V-shaped cam part and projecting cam part.
Generally, in a form of a push-button type tuning apparatus, a push-button assembly having a push-button plate and a sliding plate respectively assembled in a vertical state thereon, is pushed, and the memorizing and reading-out of the selected station is performed by urging a wedge-shaped memory piece rotatably supported on the sliding plate to make contact with a pair of shafts provided on a freely rotatable frame, and restricting the mutual relationship between the positions of the wedge-shaped memory piece and the above frame. In another form of a push-button type tuning apparatus, a push-button assembly having a push-button plate and a sliding plate respectively assembled in a horizontal state thereon, is pushed, and the memorizing and reading-out of the selected station is performed by urging a memory piece in a direction perpendicular to the direction of the above pushing of the push-button assembly to make contact with a cam plate provided freely slidable and horizontally, and restricting the mutual relationship between the positions of the memory piece and the cam plate. In the above described forms of push-button type tuning apparatuses, the former arranges the push-button plate and the sliding plate vertically, and hence, the thickness of the apparatus becomes large. Accordingly, the second form of push-button type tuning apparatus is frequently used these days because of its thin construction.
A push-button type tuning apparatus provided with a V-shaped cam part (the pitch of the V-shaped cam part in the left and right directions is designated by P) at a part, of the above cam plate which is freely slidable in the left and right directions, corresponding to each of the push-button assemblies, and performs the memorizing and reading-out of the selected station when the memory piece of the push-button assembly makes contact with the above V-shaped cam part, has been proposed as the above thin-type push-button type tuning apparatus. In this previously proposed apparatus, if the memorizing of a station is performed when the memory piece makes contact with a certain point on one side of the V-shape of the cam plate (at a point separated from the vertex of the V-shaped by a distance l1) and rotated, and the memory piece then makes contact with the other side of the V-shape of the cam plate (at a point separated from the vertex of the V-shape by a distance l2) upon reading-out of the selected station, the cam plate accordingly slides by a distance (l1+l2) in one move. When (l1+l2) is larger than P/2, the memory piece disengages from the corresponding V-shaped cam part upon reading-out of the selected station, and thus, the value (l1+l2) must be smaller than P/2. Accordingly, there was a disadvantage in that the tuning accuracy was easily degraded, since the maximum sliding quantity of the cam plate is limited to a relatively small quantity, mainly, P/2.
Furthermore, in the conventional push-button type tuning apparatus described above, the memory piece which is already locked, makes contact with the cam plate upon pushing in of the push-button assembly, and forcibly returns the cam plate into the position upon memorizing of the desired station. However, in this push-button type tuning apparatus of the above described construction, the cam plate must be slidable with a small load. Thus, normally, predetermined clutch changeover means is operated relative to the push-in operation of the push-button assembly, to put the clutch means between the cam plate and the manual tuning part in a non-transferring state, and put the cam plate in the above small load slidable state. But in this normal construction, the above clutch changeover means operates to put the cam plate in the small load slidable state even when the push-button assembly is pushed in upon reading-out of the selected station. Accordingly, there was a disadvantage in that the cam plate which is in advance positioned at a predetermined position by the manual tuning operation, is slightly displaced by shocks such as the shock exerted from the outside, and the shock introduced when the memory piece makes contact, to result in an incorrect memory operation by the memory piece.